A polymer of conjugated diene monomer such as 1,3-butadiene or isoprene, or a copolymer with a vinyl aromatic monomer such as styrene that may be copolymerized with the conjugated diene monomer, have been widely used as an elastomer.
With the double bonds within internal polymer chain, these polymers may be vulcanized but their durability and oxidation resistances are poor.
Meantime, some block copolymers prepared from conjugated diene monomer and vinyl aromatic monomer so-called a thermoplastic elastomer have been used as a modifier to improve an impact resistance for transparent resin or polyolefin and polystyrene resin, without vulcanization.
These polymers containing olefinic unsaturated double bonds may be advantageously utilized due to their easy cross-linking reaction, while their double bonds are responsible for some stability problems such as thermal resistance, oxidation resistance and weatherability.
Under such circumstances, these polymers have been applied within the restricted range, which is an only in-house uses.
In general, in an effort to improve the durability and oxidation resistance of a polymer having unsaturated double bonds, the unsaturated double bonds may be partially or completely saturated by the addition of hydrogen in a polymer.
Various methods to hydrogenate some polymers having olefinic unsaturated double bonds have been reported but they could be classified into two main methods.
The first method is to use a heterogeneous catalyst, while the second one is to use Ziegler catalyst or a homogeneous catalyst belonging to organometallic compounds such as rhodium or titanium.
From the two methods, the hydrogenation based on a heterogeneous catalyst is performed in such a manner that a polymer of unsaturated double bonds dissolved in a suitable solvent is contacted with hydrogen in the presence of a heterogeneous catalyst. However, this method has recognized several disadvantages in that:                a) A contact between reactants and catalyst is not easily made due to the fact that the steric hindrance of a polymer is large and its relative viscosity is higher;        b) In addition due to the strong physical adsorption of a polymer to the surface of a catalyst, it is very difficult to detach the already hydrogenated polymer from the catalyst, thus it makes other unsaturated polymers hard to reach the active site of a catalyst; therefore, for the complete hydrogenation of the unsaturated double bonds of a polymer, a large amount of catalyst is required with severe reaction conditions such as a higher temperature and pressure and as a result, the decomposition and gelation of a polymer may sometimes occur;        c) In particular, the selective hydrogenation of olefinic polymer in a copolymer containing conjugated diene monomer and vinyl aromatic monomer under such severe reaction conditions is extremely difficult, since the unsaturated double bonds of an aromatic compound could be simultaneously hydrogenated;        d) In addition, the physical separation of a catalyst contained in a hydrogenated polymer solution is extremely difficult; a certain heterogeneous catalyst is strongly attached to a polymer so that its complete removal is impossible.        
By contrast, the hydrogenation based on a homogeneous catalyst has the following advantages in that:                a) The activity is much higher than the one of a heterogeneous catalyst and with a small amount of catalyst, a higher yield of final product may be expected under a mild condition such as a low temperature and pressure;        b) Further, under the mild hydrogenation conditions, the selective hydrogenation of unsaturated olefinic double bonds could be performed in a copolymer chain containing vinyl aromatic monomer and conjugated diene without the hydrognation of unsaturated aromatic double bonds.        
Nonetheless, the process for hydrogenating the unsaturated double bonds of a conjugated diene polymer in the presence of a homogeneous catalyst has some drawbacks in that a) the stability of a catalyst itself is low, and b) the separation of a decomposed catalyst from the hydrogenated polymer is extremely difficult.
Meantime, several methods of hydrogenating or selectively hydrogenating the unsaturated double bonds of a conjugated diene polymer has been reported; for example, the U.S. Pat. Nos. 3,494,942, 3,670,054 and 3,700,633.
These patents have described the methods of using some catalysts containing some metals belonging to the groups of 8, 9 and 10, being published in the prior art or their precursors, in an effort to hydrogenate or selectively hydrogenate the ethylenic unsaturated double bonds of a polymer and copolymer containing aromatic and ethylenic unsaturated double bonds.
According to the process of the aforementioned patent, a catalyst was prepared using some metals belonging to the groups of 9 and 10, especially nickel or cobalt compound, with a suitable reducing agent such as alkyl aluminum. Other suitable reducing agent described in the prior art include some metals belonging to the groups of 1, 2 and 13, especially lithium, magnesium and aluminum allyls or hydrides according to the prior art. Hence, some metals belonging to the groups of 1, 2 and 13 and other metals belonging to the groups of 8, 9 and 10 are mixed in the molar ratio of 0.1:1 to 20:1, more preferably in the molar ratio of 1:1 to 10:1.
The U.S. Pat. No. 4,501,857 has disclosed that the selective hydrogenation of unsaturated double bonds in a conjugated diene polymer resulting from its polymerization may be effected in the presence of at least one bis(cyclopentadienyl) titanium compound or at least one organo lithium compound.
Further, the U.S. Pat. No. 4,980,421 has disclosed that a polymer may have a similar hydrogenation activity using an alkoxy lithium compound directly or a reaction mixture between an organs lithium compound and alcohol or phenol, or its combined compound with bis(cyclopentadienyl)titanium compound. It describes that even though a small amount of catalyst is used, the catalyst is effectively active, while any washing process to remove the residual catalyst is not necessary.
The U.S. Pat. No. 4,673,714 has disclosed that bis(cyclopentadienyl) titanium compound can preferably hydrogenate unsaturated double bonds in a conjugated diene in the absence of alkyl lithium; The detailed example of such titanium compound included bis(cyclopentadienyl)titanium diaryl compound, and the most advantage of this catalyst system is that a hydrocarbon lithium compound as a reducing agent is not used.
Also, the U.S. Pat. No. 5,039,755 has disclosed a process for the hydrogenation of conjugated diene polymer which comprises polymerizing or copolymerizing one conjugated diene monomer with an organo alkali metal polymerization initiator in a suitable solvent thereby forming a living polymer, terminating the polymerization by the addition of hydrogen; The selective hydrogenation of unsaturated double bonds in the conjugated diene units of the aforementioned terminated polymer was conducted in the presence of (C5H5)2TiR2 (R is an arylalkyl group) catalyst.
The U.S. Pat. No. 5,243,986 has disclosed that the double bonds of conjugated diene units or a styrene-butadiene-isoprene copolymer may be selectively hydrogenated using a specific titanocene compound and reducing agent.
Further, the U.S. Pat. No. 5,321,175 has disclosed a process of hydrogenating a conjugated diene polymer in the presence of homogeneous catalysts which contain Cp2Ti(PhOR)2 (where, Cp is a cyclopentadienyl group; OR is an alkoxy compound containing 1 to 4 carbon atoms) or Cp2TiR2 (where, R is a CH2PPh2).
Also, another process of hydrogenating an olefinic monomer using a mixture of Cp2TiCl2 or (C6H10(p-CH3OC6H4)C5H4)2TiCl2 as a catalyst and a high-activity alkali metal hydride(MH) prepared in solution has been disclosed [ref.: Journal of Organometallic Chemistry, 382 (1990) 69-76].
However, the aforementioned homogeneous catalyst has recognized some disadvantages in that a) in general, since it is extremely sensitive to an environment, the catalyst is easily inactivated in the air or in the presence of moisture, and b) the hydrogenation activity is greatly affected by the reducing state of the catalyst. Since there is trend that the reproducibility of hydrogenation is reduced in the long run, the prior art has found it difficult to obtain a hydrogenated polymer with a high hydrogenation rate and reproducibility simultaneously.
In addition, there is another trends that the active ingredients of the catalyst are easily converted to inactive ones, when the reaction proceeds. This may result in reducing the hydrogenation yield, thus being responsible for poor reaction reproducibility. Such trend will badly affect the hydrogenation of a polymer designed to improve the durability and oxidation resistance of a polymer. Furthermore, the hydrogenation rate of the homogeneous catalyst is much affected depending on its stability during the hydrogenation.
As noted in the above, it is prerequisite to overcome these drawbacks in adequately applying such homogeneous catalysts to the hydrogenation of a polymer in the industrial level. Thus, there is need to develop a highly active hydrogenation catalyst with better stability and reproducibility.